The invention generally relates to improvements in recycle gas cooler systems for gas-phase polymerization processes that reduce the tendency for cooler fouling.
Advances in polymerization and catalysts have produced new polymers having improved physical and mechanical properties useful in a wide variety of products and applications. With the development of new catalysts, the choice of polymerization process, such as solution, slurry, high pressure or gas phase, for producing a particular polymer has been greatly expanded. Advances in polymerization technology have also provided more efficient, highly productive and economically enhanced processes.
One technique for polymer production involves a gas-phase polymerization process. In gas-phase polymerization processes, recycle gas is typically withdrawn from the polymerization reactor and passed through a cooler for removal of reaction heat and optionally also for partial condensing. After cooling, the recycle gas is typically returned to the polymerization reactor. The cooler is typically a shell-and-tube heat exchanger, for example, with cooling water on the shell side and the recycle gas on the tube side. Because the recycle gas may contain catalyst particles and polymer particles, there is a possibility of continued polymerization in the cooler, which can lead to polymer formation in the cooler, particularly at sections where there may be relatively slow particle velocities. The polymer formed in the cooler may accumulate on the cooler walls and lead to fouling. As a result of this fouling, pressure drop across the cooler may increase. In addition, the fouling may cause a reduction in the heat-transfer efficiency of the cooler and, thus, a reduction in production rate for the polymerization process. If problems associated with fouling are severe enough, the polymerization reactor may need to be shut down for cooler cleaning. However, there are considerable costs associated with reactor shut down, including the loss of production time, for example.
Accordingly, there exists a need for improved gas-phase polymerization processes that can reduce cooler fouling so as to maximize operation time of the cooler with resultant increased operating time for the polymerization reactor.